Electronic and magnetic properties of the ferromagnetic superconductor UCoGe

The electronic structure and x-ray magnetic circular dichroism (XMCD) spectra of the ferromagnetic superconductor UCoGe at the U N₄,₅, Ge and Co K and Co L₂,₃ edges were investigated theoretically from first principles, using the fully relativistic Dirac linear muffin-tin orbital band structure method. The electronic structure is obtained with the local spin-density approximation (LSDA), as well as with a generalization of the LSDA+ U method which takes into account the non-diagonal occupation matrix (in spin indexes) of localized electrons. A stable ferromagnetic ground state was found. The uranium total magnetic moment is quite small (about −0.171μB) in the LSDA approximation as a result of almost complete cancellation between the spin magnetic moment of 0.657μB and the opposite orbital magnetic moment of −0.828μB, resulting from strong spin-orbit coupling at the uranium site. Valency of U ion in UCoGe is close to 3+. The ratio orbital and spin magnetic moments M l/M s ranged from 1.163 in the GGA approach up to 2.456 for the LSDA+ U calculations is smaller than the corresponding ratio for the free ion U³⁺ value (2.60), it can indicate a significant delocalization of the 5 f-electron states due to the hybridization of the U 5f electrons with the conduction band and Co 3d electrons. The line shape of the dichroic spectra at the U M₅ and M₄ edges predicted by considering the magneto-optical selection rules as well as the occupation and the energy sequence of the mj-projected partial densities of states. The theoretically calculated XMCD spectra at the U M₄,₅, Ge and Co K and Co L₂,₃ edges are in good agreement with the experimentally measured spectra

Electronic structure, Fermi surface and dHvA effect in YIn₃, LuIn₃, and YbIn₃

The electronic structure, Fermi surface, angle dependence of the cyclotron masses and extremal cross sections of the Fermi surface of RIn₃ (R = Y, Lu, and Yb) compounds were investigated from first principles using the fully relativistic Dirac linear muffin-tin orbital method. The effect of the spin-orbit (SO) interaction and Coulomb repulsion U in a frame of the LDA+SO+U method on the Fermi surface, orbital dependence of the cyclotron masses, and extremal cross sections of the Fermi surface are examined in details. A good agreement with experimental data of cyclotron masses and extremal cross sections of the Fermi surface was achieved

Electronic structure and x-ray magnetic circular dichroism in A₂CrB′O₆ (A = Ca, Sr; B′ = W, Re, and Os) oxides

A systematic electronic structure study of A₂CrB′O₆ (A = Ca, Sr; B′ = W, Re, and Os) has been performed by employing the local spin-density approximation (LSDA) as well as the GGA and LSDA + U methods using the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. We investigated the effects of the subtle interplay among the spin-orbit coupling, electron correlations, and lattice distortion on the electronic structure of the double perovskites. First principles calculations predict that Sr₂CrOsO₆ is (before considering spin-orbit coupling) actually a ferrimagnetic semimetal with precisely compensating spin moments, or spin-asymmetric compensated semimetallic ferrimagnet in which the electrons and holes are each fully polarized and have opposite spin directions, in spite of a zero net moment and hence no macroscopic magnetic field. Spin-orbit coupling degrades this by giving a nonzero total moment, but the band structure is little changed. Therefore, the observed saturation moment of ferrimagnetic Sr ₂CrOsO ₆ is entirely due to spin-orbit coupling. The x-ray absorption spectra and x-ray magnetic circular dichroism at the W, Re, Os, and CrL₂,₃, and Cr and O K edges were investigated theoretically from first principles. A qualitative explanation of the XMCD spectra shape is provided by the analysis of the corresponding selection rules, orbital character and occupation numbers of individual orbitals. The calculated results are in good agreement with experimental data. The complex fine structure of the CrL₂,₃ XAS in Sr₂CrWO₆ and Sr₂CrReO₆ was found to be not compatible with a pure Cr³⁺ valency state. The interpretation demands mixed valent states. We found that possible oxygen vacancies lead to a mixed valency at the Cr site, double peak structure at the CrL₂,₃ edges and reduce the saturation magnetization in Sr₂CrWO₆ and Sr₂CrReO₆

Electronic structure, phonon spectra and electron–phonon interaction in ScB₂

The electronic structure, Fermi surface, angle dependence of the cyclotron masses and extremal cross sections of the Fermi surface, phonon spectra, electron–phonon Eliashberg and transport spectral functions, temperature dependence of electrical resistivity of the ScB₂ diboride were investigated from first principles using the fully re-lativistic and full potential linear muffin-tin orbital methods. The calculations of the dynamic matrix were carried out within the framework of the linear response theory. A good agreement with experimental data of electron–phonon spectral functions, electrical resistivity, cyclotron masses and extremal cross sections of the Fermi sur-face was achieved

Electronic structure and x-ray magnetic circular dichroism in the Mn₃CuN perovskite

The electronic and magnetic structures of Mn₃CuN are investigated theoretically from first principles using the fully relativistic Dirac LMTO band structure method. Mn₃CuN possesses a magnetic phase transition at TC = 143 K from a high temperature paramagnetic phase to a low temperature ferromagnetic one with a noncollinear magnetic structure. The transition is accompanied by a structural change from the cubic to the tetragonal lattice. In low temperature phase two Cu moments and two Mn moments (Mn₂ and Mn₃) ferromagnetically align along the c axis while other four Mn1 magnetic moments are canted from the c axis to [111] direction by angle Q= ±76.2. The x-ray absorption spectra and x-ray magnetic circular dichroism (XMCD) spectra of Mn₃CuN are investigated theoretically from first principles. The origin of the XMCD spectra in the Mn₃CuN compound is examined. The calculated results are compared with the experimental data

Electronic structure and x-ray magnetic circular dichroism of Mn-doped TiO₂

The electronic structure of (Ti,Mn)O₂ diluted magnetic semiconductors was investigated theoretically from first principles using the fully relativistic Dirac linear muffin-tin orbital band structure method. The electronic structure was obtained with the local spin-density approximation taking into account strong Coulomb correlations in the frame of the LSDA + U approximation. The x-ray absorption spectra and x-ray magnetic circular dichroism spectra at the Mn and Ti L₂,₃ and O K edges were investigated theoretically from first principles. The origin of the XMCD spectra in these compounds was examined. The calculated results are compared with available experimental data

X-ray magnetic circular dichroism in Co₂FeGa: First-principles calculations

The electronic structure and x-ray magnetic circular dichroism (XMCD) spectra of the Heusler alloy Co₂FeGa were investigated theoretically from first principles, using the fully relativistic Dirac linear MT-orbital (LMTO) band structure method. Densities of valence states, orbital and spin magnetic moments are analyzed and discussed. The origin of the XMCD spectra in the Co₂FeGa compound is examined. The calculated results are compared with available experimental data

X-ray magnetic circular dichroism in d and f ferromagnetic materials: recent theoretical progress. Part I

The current status of theoretical understanding of the x-ray magnetic circular dichroism (XMCD) of 3d compounds is reviewed. Energy band theory based upon the local spin-density approximation (LSDA) describes the XMCD spectra of transition metal compounds reasonably well. Examples which we examine in detail are XPt₃ compounds (with X = V, Cr, Mn, Fe, Co, and Ni) in the AuCu₃ structure, Heusler compounds Co₂MnGe, Co₂NbSn, and compounds with noncollinear magnetic structure IrMnAl and Mn₃ZnC. Recently achieved improvements for describing the electronic and magnetic structures of 3d compounds are discussed

X-ray magnetic circular dichroism in d and f ferromagnetic materials: recent theoretical progress. Part I

The curreThe current status of theoretical understanding of the x-ray magnetic circular dichroism (XMCD) of 4 f and 5 f compounds is reviewed. Energy band theory based upon the local spin-density approximation (LSDA) describes the XMCD spectra of transition metal compounds with high accuracy. However, the LSDA does not suffice for lanthanide compounds which have a correlated 4 f shell. A satisfactory description of the XMCD spectra could be obtained by using a generalization of the LSDA, in which explicitly f electron Coulomb correlation are taken into account (LSDA + U approach). As examples of this group we consider GdN compound. We also consider uranium 5 f compounds. In those compounds where the 5 f electrons are rather delocalized, the LSDA describes the XMCD spectra reasonably well. As example of this group we consider UFe₂. Particular differences occur for the uranium compounds where the 5 f electrons are neither delocalized nor localized, but more or less semilocalized. Typical examples are UXAl (X = Co, Rh, and Pt), and UX (X = S, Se, Te). The semilocalized 5 f ’s are, however, not inert, but their interaction with conduction electrons plays an important role. We also consider the electronic structure and XMCD spectra of heavy-fermion compounds UPt₃, URu₂Si₂, UPd₂Al3₃, UNi₂Al₃, and UBe₁₃ where the degree of the 5 f localization is increased in comparison with other uranium compounds. The electronic structure and XMCD spectra of UGe₂ which possesses simultaneously ferromagnetism and superconductivity also presented. Recently achieved improvements for describing 5 f compounds are discussed

Electronic structure and magneto-optical Kerr effect in UCuAs₂

The optical and magneto-optical (MO) spectra of the ternary compound UCuAs₂ are investigated theoretically from first principles, using the fully relativistic Dirac linear-muffin-tin-orbital band structure method. The electronic structure is obtained with the local spin-density approximation (LSDA), as well as with the so-called LSDA+U approach. Better agreement between the theoretically calculated and the experimentally measured MO Kerr spectra is found with the LSDA+U approximation. The origin of the Kerr rotation in the compound is examined